Active matrix liquid crystal display having insulating layer larger than display electrode and smaller than video line in thickness

ABSTRACT

An active matrix liquid crystal display improves its contrast by suppressing irregularity of an alignment film caused by video lines thereby reducing reverse regions on a display electrode. The active matrix liquid crystal display has first and second opposite substrates, a video line, an active element and a display electrode which are directly or indirectly formed on the first substrate, and an alignment film which is formed on or above the video line, the active element and the display electrode. The alignment film is so formed that its surface is at an angle of inclination of not more than 10.5° with respect to the display electrode surface between the video line and the display electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active matrix liquid crystal displaywhich is applied to an office automation apparatus or a measuringinstrument as a display.

2. Description of the Background Art

A liquid crystal display may present such a phenomenon, called reversal,that a region exhibiting orientation which is different from that in adisplay electrode, i.e., a reverse region, is formed around the displayelectrode to reduce the contrast of the liquid crystal display.

As to the reversal of a simple matrix liquid crystal display, known aresuch a phenomenon that strip-shaped reverse regions extending from adisplay electrode in three directions are formed by an electric fieldwhich obliquely extends between opposite electrodes (Japanese PatentLaying-Open No. 55-74517 (1980)), and a phenomenon causing strip-shapedreverse regions along two sides of a display electrode on its inclinedsurfaces (Japanese Patent Laying-Open No. 58-50514 (1983)).

On the other hand, a method of preparing a liquid crystal displayincluding a step of rubbing an alignment film from a display electrodetoward an active element (Japanese Patent Laying-Open No. 60-178425(1985)) is proposed as a method of eliminating a reverse region in anactive matrix liquid crystal display.

Even if the method described in this prior art is employed, however, thereversal in the active matrix liquid crystal display is not necessarilycompletely eliminated.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an active matrix liquidcrystal display having improved visibility by overcoming theaforementioned disadvantage of the prior art and suppressingirregularity of an alignment film caused by video lines which areincreased in thickness due to requirement for low resistance, therebyreducing reverse regions on a display electrode.

The inventor has studied the aforementioned reversal in the conventionalactive matrix liquid crystal display, and discovered that irregularityof an alignment film provided on video lines which are increased inthickness due to requirement for low resistance is largely concernedwith occurrence of the reversal.

With reference to FIGS. 10 to 12, the reversal in the conventionalactive matrix liquid crystal display is now described.

FIG. 10 is a plan view showing the conventional active matrix liquidcrystal display. As shown in FIG. 10, a picture signal is supplied to A1video lines 1 of 2 μm in thickness by a horizontal scanning shiftresistor of polycrystalline Si which outputs successively shiftedpulses, while a scanning signal is supplied to Ta scanning lines 2 of2000 Å in thickness by a vertical scanning shift resistor ofpolycrystalline Si every horizontal scanning period.

Further, coplanar TFTs 3 of polycrystalline Si are formed in thevicinity of intersections between the scanning lines 2 and the videolines 1, for controlling cutoff and conduction of the picture signalwhich is transmitted to ITO display electrodes 4 of 700 Å in thicknessfrom the video lines 1 through the TFTs 3.

When nematic liquid crystals are employed in practice in the activematrix liquid crystal display shown in FIG. 10, it is necessary toprovide a pair of polarizing plates on outer sides of the stackingdirection, while these polarizing plates are not shown in FIG. 10.Throughout this specification, description is made with omission of suchpolarizing plates.

When an alignment film of 1000 Å in thickness which is provided on thedisplay electrodes 4 enclosed with the scanning lines 2 and the videolines 1 is rubbed in a rubbing direction 5 from the TFTs 3 serving asactive elements toward the display electrodes 4, reverse regions 6 areformed as shown in a hatched manner in FIG. 10.

In general, a boundary of the reverse region 6 in each display electrode4 is called a transition line 7, and the distances between thetransition line 7 and respective sides of the display electrode 4 aregenerally different from each other. In other words, the reverse region6 is varied in width on the sides of the video and scanning lines 1 and2.

Assuming that the surface of the alignment film which is formed on eachdisplay electrode 4 has an angle θ of inclination of 80°, the widths ofthe reverse region 6 are expressed by dropout distances a and b on thesides of the video and scanning lines 1 and 2 in FIG. 10 as follows:

                  TABLE 1    ______________________________________    Angle of   Dropout Distance                            Dropout Distance    Inclination               on Video Line Side                            on Scanning Line Side    θ    a            b    ______________________________________    80         10           8    ______________________________________

When the display electrode is originally for black display in Table 1,the reverse region in white display, to reduce visibility of the liquidcrystal display. Such white display of the reverse region is anunpreferable phenomenon, and hence expressed as "dropout" as shown inTable 1.

It is clearly understood from Table 1 that the dropout distance a on theside of the video line 1 which is ten times the scanning line 2 inthickness has a larger value of 10 μm as compared with the dropoutdistance b on the side of the scanning line 2.

Accordingly, only the dropout distance a on the video line side is notedin the following description.

Referring to FIG. 10, the surface state of the alignment film is hard tounderstand. Therefore, the following description is made with referenceto FIG. 11 showing a section of the active matrix liquid crystal displaytaken along the line XI--XI in FIG. 10.

FIG. 11 is a sectional view of the aforementioned active matrix liquidcrystal display causing the phenomenon called reversal or dropout. Asshown in FIG. 11, the surface of a portion of the alignment film 8 whichis positioned between the display electrode 4 and the video line 1 isinclined at an angle θ of 80° toward the video line 1.

In the vicinity of the aforementioned inclined surface of the alignmentfilm 8, liquid crystals 9 are so reversely arranged that the reverselyarranged liquid crystal molecules reach the interior of an upper regionof the display electrode 4. The reverse region 6 on the side of thevideo line 1 shown in FIG. 10 is formed by the reversely arranged liquidcrystal molecules which are positioned on the upper region of thedisplay electrode 4, leading to observation of the dropout having theaforementioned dropout distance a.

In the aforementioned active matrix liquid crystal display, a gateinsulating film 10 of silicon oxide and a TFT substrate 11 of glass arearranged under the display electrode 4. A counter alignment film 13 anda counter substrate 14 are formed on both sides of a counter electrode12, which is opposed to the display electrode 4, along the stackingdirection. Further, polarizing plates (not shown) are arranged on bothsides of a pair of substrates, consisting of the TFT substrate 11 andthe counter substrate 14, along the stacking direction.

In order to indicate the degree of the aforementioned dropout on thedisplay electrode 4, description is now made with reference to FIG. 12through a distance d from an end 4a of the display electrode 4. Thedistance d from the end 4a of the display electrode 4 has beencalculated from an actual distance in case of preparing theaforementioned polarizing plates from HC2-8218 (trade name) by KabushikiKaisha Sanrittsu having parallel transmittance of 31% and orthogonaltransmittance of 3% at a wavelength of 580 nm by expressing the paralleltransmittance of 31% in terms of transmittance T of 100%.

While FIG. 11 illustrates the liquid crystals 9 in the form of amonomolecular provided between the alignment film 8 and the counteralignment film 13, a plurality of liquid crystal molecules are arrangedbetween the alignment film 8 and the counter alignment film 13 along thedirection of thickness in practice. FIG. 11 illustrates the liquidcrystals 9 in the aforementioned manner in order to clearly show theinfluence exerted by the alignment film 8. FIGS. 1, 3 and 5 to 8 alsosketchily illustrate liquid crystal molecules, for the same reason asthe above.

FIG. 12 is a characteristic diagram showing the dependence of thetransmittance T on the distance d from the end 4a of the displayelectrode 4. Referring to FIG. 10, the width (the dimension along thedistance d) of the display electrode 4 is set at 100 μm, while the videoline 1 is set as being approximate on the side having the large distanced.

As shown in FIG. 12, the transmittance is abruptly changed around thedistance d of 94 to 95 μm, and when the distance d is in excess of this,it is understood that the transmittance curve becomes to be a paraboliccurve, the upper side of which is a convex side, so that the reverseregion wherein the transmittance is about 70% at most is formed. Inpractice, the distance d causing the abrupt change of the transmittanceT in the aforementioned manner was 94 μm in picture processing data, and95 μm in visual observation.

The difference of about 1 μm between the picture processing data and thevisual data is conceivably caused since the human eyes are sensitive toa brighter region and tend to observe the boundary on the average.

As understood from FIG. 12, the transmittance T is increased in thereverse region, in correspondence to the phenomenon called "dropout".

There is such a tendency that the contrast of the liquid crystal displayis necessarily reduced when a reverse region or a dropout phenomenon iscaused on its display electrode.

According to a wide aspect of the present invention, provided is anactive matrix liquid crystal display comprising a first substrate, adisplay electrode which is formed on the first substrate, an electrodewhich is formed at least either on a part under or on a side of thedisplay electrode on the first substrate, an alignment film which isformed to cover the display electrode, a second substrate which isopposed to the first substrate, a counter alignment film which is formedon a surface of the second substrate facing the first substrate, andliquid crystals which are held between the alignment film and thecounter alignment film. The alignment film has a surface which isinclined from a flat surface portion on the display electrode toward aportion above that provided with the electrode, and an angle ofinclination of the inclined surface of the alignment film is not morethan 10.5°, preferably not more than 7°, with respect to the flatsurface portion.

Although the active matrix liquid crystal display according to thepresent invention an inclined surface is formed in the alignment filmdue to existence of the electrode formed at least either on a part underor on a side of the display electrode, the alignment film surface issmoothly inclined at an angle of not more than 10.5°, preferably 7°, ashereinabove described. Therefore, the reversal energy of the liquidcrystals which are in contact with the smoothly inclined portion of thealignment film is extremely reduced. Consequently, formation of reverseregions is effectively suppressed not only on a scanning line side buton the video line side in an upper region of the display electrode.Thus, the ratio of a light transmitting portion to a light interceptingportion in transmittance, i.e., the contrast, is so improved that anactive matrix liquid crystal display which can display clearer imagescan be provided. In the active matrix liquid crystal display accordingto the present invention, therefore, the display electrode can befurther approached to the video line, thereby improving the numericalaperture of the liquid crystal display.

In the present invention, it is assumed that the aforementioned flatsurface portion of the alignment film on the display electrode indicatesa flat portion of the surface of the alignment film which is positionedon a principal plane of the display electrode, and that theaforementioned inclined surface indicates an inclined region of thesurface of the alignment film from a portion which is inclined withrespect to the flat surface portion due to the presence of the electrodeto a portion which is parallel to the flat surface portion again.

According to a specific aspect of the present invention, the electrodewhich is formed at least either on a part under or on a side of thedisplay electrode is a video line, and this video line is arranged on aside of the display electrode. In this case, it comes to that theinclined surface is formed from the alignment film located on thedisplay electrode toward an upper portion of the video line which isarranged on a side of the display electrode.

According to another specific aspect of the present invention, thealignment film which is in contact with the liquid crystals is formed bya single-layer film. Thus, a flat alignment film is formed by a singlelayer, whereby elimination of reverse regions can be achieved in asimple structure.

According to still another specific aspect of the present invention, aSOG layer which is prepared by a spin-on-glass method are formed betweenthe display electrode and the alignment film. According to thisstructure, the transmittance can be improved since the smooth SOG filmis almost achromatic. In addition, a plurality of SOG layers may beformed between the display electrode and the alignment film.

According to a further specific aspect of the present invention, aninsulating layer which is larger than the display electrode and smallerthan the video line in thickness is further provided between the videoline and the display electrode. In this case, the insulating layerhaving an intermediate thickness is formed between the video line andthe display electrode, whereby the alignment film which is formed on thedisplay electrode can be reduced in thickness, thereby improving thetransmittance.

According to a further specific aspect of the present invention, a BPSGlayer (borophosphosilicate glass layer) and an SOG layer are formedbetween the display electrode and the alignment film, whereby change inwithstand voltage of the insulating film can be reduced and thewithstand voltage across the display electrode and the counter electrodecan be improved.

According to a further specific aspect of the present invention, anelectrode which is partially formed under the aforementioned displayelectrode is an storage capacitive electrode for supplying an storagecapacitive to pixels. In this case, the alignment film rises on thedisplay electrode due to the partial presence of the storage capacitiveelectrode under the display electrode, to form the aforementionedinclined surface. In order to electrically insulate the storagecapacitive electrode from the display electrode, an insulating layer isprovided between these electrodes.

Also in the inclined surface which is formed on the alignment film dueto the presence of the storage capacitive electrode under the displayelectrode, the angle of inclination with respect to the flat surfaceportion of the alignment film is set to be not more than 10.5°,preferably not more than 7°. Thus, it is possible to provide an activematrix liquid crystal display which can effectively suppress formationof reverse regions, effectively improve the ratio of a lighttransmitting portion to a light intercepting portion in transmittance,i.e., the contrast, and display clear images.

According to a further specific aspect of the present invention, thestorage capacitive electrode consists of a polycrystalline siliconlayer, the insulating layer consists of a composite layer which isformed by stacking BPSG and SOG layers with each other. In this case,the BPSG layer is deposited on the polycrystalline silicon layer whichcan be heated, whereby flattening is facilitated by thermal melting. Inaddition, the BPSG layer forms the insulating layer, whereby thewithstand voltage across the display and storage capacitive electrodescan be improved.

According to a further specific aspect of the present invention, asubstrate covering film is formed between the worked polycrystallinesilicon layer and the first substrate. Thus, the substrate covering filmis present under the worked polycrystalline silicon layer, whereby thesubstrate is hardly opaqued by etching or influenced by irregularity.Thus, a bad influence exerted by etching of the polycrystalline siliconlayer or irregularity of the substrate can be reduced.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an active matrix liquid crystal displayaccording to an embodiment of the present invention, which is providedwith an alignment film having a smooth inclined surface;

FIG. 2 is a characteristic diagram showing change of a dropout distancein relation to an angle of inclination of an alignment film;

FIG. 3 is a sectional view showing an active matrix liquid crystaldisplay according to another embodiment of the present invention, whichis provided with an SOG layer;

FIG. 4 illustrates transmittance characteristics of the liquid crystaldisplay according to the embodiment shown in FIG. 3;

FIG. 5 is a sectional view of an active matrix liquid crystal displayaccording to still another embodiment of the present invention, which isprovided with an insulating layer between electrodes;

FIG. 6 is a plan view showing an active matrix liquid crystal displayaccording to a further embodiment of the present invention, which isprovided with a BPSG layer;

FIG. 7 is a plan view showing an active matrix liquid crystal displayaccording to a further embodiment of the present invention, which isprovided with a p-Si layer;

FIG. 8 is a sectional view showing an active matrix liquid crystaldisplay according to a further embodiment of the present invention;

FIG. 9 is a plan view showing a principal part of the active matrixliquid crystal display appearing in FIG. 8;

FIG. 10 is a plan view for illustrating a conventional active matrixliquid crystal display, which is formed with reverse regions;

FIG. 11 is a sectional view of the conventional active matrix liquidcrystal display, which is formed with reverse regions; and

FIG. 12 illustrates transmittance characteristics on a display electrodein the conventional active matrix liquid crystal display.

FIG. 13 illustrates transmittance-to-distance characteristic diagramshowing such a state that a region having abnormal transmittance Tformed around a display electrode closer to a video line is reduced dueto presence of a SOG layer and a BPSG layer and that the abnormaltransmittance T becomes to be small.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a partially fragmented sectional view of an active matrixliquid crystal display according to an embodiment of the presentinvention, in correspondence to FIG. 11 showing the conventional liquidcrystal display appearing in FIG. 10.

A gate insulating film 10 is formed on a quartz glass TFT substrate 11having surface roughness of not more than 0.3 μm for serving as a firstsubstrate. The TFT substrate is so structured that a thin filmtransistor as an active circuit element is formed on a substrate member.The transistor controls transmission of video signals from a video linedescribed hereinafter. A plurality of transparent display electrodes 4of ITO, which are 700 Å in thickness, are provided on the gateinsulating film 10. The display electrode 4 is electrically connected tothe thin film transistor. A single-layer alignment film 8 of polyimidehaving a smooth surface, which characterizes the present invention, isprovided to cover the display electrodes 4.

On the other hand, a transparent counter electrode 12 of ITO is formedon the overall lower surface of a low alkali glass counter substrate 14serving as a second substrate, while a counter alignment film 13 ofpolyimide is provided on the counter electrode 12. Liquid crystals 9 arecharged between the alignment film 8 and the counter alignment film 13.

The alignment film 8 has a thickness of 2 μm, and is formed on theoverall surface of the TFT substrate 11, except a portion of ITO whichis connected to the counter electrode 12 on the TFT substrate 11.

A video line 1 is formed on a side of each display electrode 4. The planshapes of the display electrodes 4 and the video lines 1 are similar tothose shown in FIG. 10.

When a pair of polarizing plates (HC2-8218 (trade name) by KabushikiKaisha Sanrittsu) (not shown in FIG. 1) are employed and the alignmentfilm 8 is formed in a thickness of 1000 Å, parallel transmittanceexpressed in terms of transmittance T of 100% is slightly reduced butstill maintained at a high level of 98%.

In a region between each display electrode 4 of 700 Å in thickness andeach video line 1 of 2 μm in thickness, the surface of the alignmentfilm 8 is set at an angle θ of inclination of 7° with respect to thedisplay electrode 4. In this case, all reverse regions on the displayelectrodes 4 disappear.

Each of scanning lines (not shown) is 2000 Å in thickness. Under such acondition that the video line 1 is larger in thickness than the scanningline, a dropout distance b on the scanning line side automaticallydisappears when a dropout distance a on the video line 1 side is gone.

Description is now made on how the aforementioned dropout distance a onthe video line 1 side in the upper region of the display electrode 4 ofthe active matrix liquid crystal display is changed with respect to theangle θ of inclination on the surface of the alignment film 8.

FIG. 2 is a characteristic diagram showing how the dropout distance a onthe video line side disappears when the angle of inclination of thealignment film 8 in the active matrix liquid crystal display accordingto the present invention is reduced.

As shown in FIG. 2, the dropout distance a on the video line side is 3.2μm in picture processing data and 1.9 μm in visual evaluation, when theangle θ of inclination is 25°.

When the angle θ of inclination is 10.5°, on the other hand, the dropoutdistance a is 1.8 μm in the picture processing data and 0.9 μm in thevisual evaluation, and inconspicuous.

When the angle θ of inclination is 7°, further, the dropout distance ais 0.1 μm in the picture processing data and 0 μm in the visualevaluation, whereby reverse regions disappear on the display electrodes.

Thus, no reversal is caused and the contrast of the active matrix liquidcrystal display is improved when the angle θ of inclination of thealignment film is set below 10.50°, preferably 7°, according to thepresent invention.

Another embodiment of the present invention is now described. FIG. 3 isa sectional view showing an active matrix liquid crystal display havinga SOG layer which is formed by a spin-on-glass method on each displayelectrode.

As shown in FIG. 3, the SOG layer 16 of SiO₂ which is formed by aspin-on-glass method cover each display electrode 4, a gate insulatingfilm 10 and each video line 1, while a polyimide alignment film 8 of3000 Å in thickness is further formed on the SOG layer 16.

The SOG layer 16 is a layer of 600 Å in thickness which is obtained byspin-coating a dilute solution of organic silicon resin at a temperatureof 20° C. and thereafter firing the same at a temperature of 180° C. fora heating time of 30 minutes.

The feature of this embodiment resides in that the SOG layer 16 which isformed by the spin-on-glass method are thickly fired in the regionsbetween the display electrode 4 and the video line 1 as compared withthose on the display electrode 4, and the surface of the alignment film8 which is deposited on the SOG layer is extremely smoothed, so that thereverse region over the display electrode disappears.

According to the structure shown in FIG. 3, the inventive active matrixliquid crystal display attains high transmittance of 99.5% when a pairof polarizing plates (HC2-8218 (trade name) by Kabushiki KaishaSanrittsu) are employed.

Illustration is made on where a reverse region appears on each displayelectrode due to presence of the SOG layer, for the purpose of contrastwith the example described with reference to FIGS. 10 to 12.

FIG. 4 is a transmittance-to-distance characteristic diagram showingsuch a state that a region having abnormal transmittance T formed arounda display electrode which is closer to a video line is reduced due topresence of an SOG layer and that the abnormal transmittance T becomesto be small.

It is understood from FIG. 4 that a white-dropout region which appearsaround the display electrode as well as the transmittance are reduced asa>a1>a2 due to increase of an alignment film and presence of the SOGlayer.

Still another embodiment of the present invention is now described.

FIG. 5 is a sectional view showing an active matrix liquid crystaldisplay according to this embodiment, having an insulating layer whichis larger than each display electrode and smaller than each video linein thickness between the display electrode and the picture electrode.

As shown in FIG. 5, an insulating layer 17 of photosensitive polyimidehaving a thickness of 1.2 μm is formed between a display electrode 4 anda video line 1, while a polyimide alignment film 8 of 2000 Å inthickness is further deposited thereon.

The insulating layer 17 of photosensitive polyimide is formed on theoverall surface of a TFT substrate by printing, and thereafter developedthrough difference between developing speeds which are varied withthicknesses.

Namely, the photosensitive polyimide tends to remain on a steppedportion between electrodes, and hence a step of leaving the remainingphotosensitive polyimide in a tapered or stepwise manner afterdevelopment is provided.

Due to formation of the insulating layer 17 and the alignment film 8 ofthe aforementioned thicknesses, reversal regions on the displayelectrodes are gone and the contrast of the liquid crystal display isimproved by 10%.

According to the structure shown in FIG. 5, the inventive active matrixliquid crystal display attains relatively high transmittance of 98.5%when a pair of polarizing plates (HC2-8218 (trade name) by KabushikiKaisha Sanrittsu) are employed.

FIG. 6 is a sectional view showing an active matrix liquid crystaldisplay according to a further embodiment of the present invention,which is provided with two insulating layers including a BPSG layer andan SOG layer between each display electrode and each video line.

Referring to FIG. 6, a BPSG layer 18 which is prepared by CVD is formedon each display electrode 4 of ITO. The BPSG layer 18 is heated to about400° C. after formation, thereby being improved in adhesion to anunderlayer and flatness on its surface.

Although an SOG layer 16 has slightly large time change of its withstandvoltage, characteristics of a driving element are stabilized withoutvarying in time due to the two-layer structure with the BPSG layer 18.

FIG. 13 illustrates transmittance-to-distance characteristic diagramshowing such a state that a region having abnormal transmittance Tformed around a display electrode closer to a video line is reduced dueto presence of a SOG layer and a BPSG layer and that the abnormaltransmittance T becomes to be small. In FIG. 13, the characteristic whenthe inclination angles are 10.5° and 7° are shown.

FIG. 7 is a sectional view of an active matrix liquid crystal displayaccording to a further embodiment of the present invention, which isprovided with two insulating layers of BPSG and SOG layers between apolycrystalline silicon layer and each display electrode.

Referring to FIG. 7, the polycrystalline silicon layer, i.e., a p-Silayer 19, serves as an storage capacitive electrode, and holds twoinsulating layers consisting of a BPSG layer 18 and an SOG layer 16between the same and a display electrode 4. Referring to FIG. 7, thethickness of the p-Si layer 19 is set at 0.3 μm, while that of liquidcrystals 9 is set at 4.6 μm. A substrate covering film 20 is shown inFIG. 7 to be disposed between p-Si layer 19 and the substrate 11.

Table 2 shows how an inclination angle 15 of surfaces of alignment films8 in the embodiment is flattened in response to thickness of SOG layer.

                  TABLE 2    ______________________________________                Thickness of SOG Layer (Å)                0       2000       4000 6000    ______________________________________    Angle of    25.0    10.5       7.0  6.5    Inclination θ    ______________________________________

In the example described with reference to FIG. 10, the alignment filmof 1000 Å in thickness has a considerably large angle of inclination.When the alignment film of 3000 Å in thickness is employed, on the otherhand, the angle θ of inclination is reduced to 25° with formation of noSOG films, as shown in Table 2.

However, it is understood from the characteristic diagram of FIG. 2 thatthe aforementioned SOG layers are necessary since the dropout distance aon the storage capacitive electrode side reaches 1.9 μm in visualobservation when the angle θ of inclination is 25°.

When a SOG layer of 2000 Å is formed, for example, the angle ofinclination is reduced to 10.5°, and the dropout distance a on thestorage capacitive electrode side is 0.9 μm with reference to FIG. 2.

When the SOG layer of 4000 Å in thickness are formed, the angle ofinclination is reduced to 7.0°, the dropout distance a on the storagecapacitive electrode side is gone from FIG. 2, and reverse regions onthe display electrodes disappear.

While Table 2 shows that the angle of inclination is 6.5° when the SOGlayer of 6000 Å in thickness are formed, it is understood that thisvalue is not much different from that in the case of 4000 Å butsubstantially saturated.

In each of the embodiments described above with reference to FIGS. 1 to7, the surface of the alignment film 8 is inclined in a region betweenthe display electrode and the video line due to the presence of thevideo line or due to the presence of the storage capacitive electrode,at a smooth angle of inclination. However, the present invention is alsoapplicable to an inclined surface of an alignment film resulting frompresence of another electrode which is partially provided under adisplay electrode or on a side of the display electrode. Such anembodiment is described with reference to FIGS. 8 and 9.

An active matrix liquid crystal display shown in FIG. 8 is substantiallysimilar in structure to that shown in FIG. 1. Therefore, portions whichare identical to those shown in FIG. 1 are denoted by the same referencenumerals, to omit redundant description.

In the active matrix liquid crystal display shown in FIGS. 8 and 9, anstorage capacitive electrode 21 is partially formed under a displayelectrode 4. Namely, the storage capacitive electrode 21 and a videoline 1 are formed on an upper surface of a TFT substrate 11 serving as afirst substrate. Further, a BPSG layer 22 is formed to cover the storagecapacitive electrode 21 and the video line 1, and an SOG layer 23 isformed on the BPSG layer 22. The BPSG layer 22 and the SOG layer 23 forman insulating layer, for electrically insulating the storage capacitiveelectrode 21 from the display electrode 4.

While the display electrode 4 is formed on the SOG layer 23, an inclinedsurface 8a is formed on a surface of an alignment film 8, since thestorage capacitive electrode 21 is partially present under the displayelectrode 4. Namely, the inclined surface 8a is formed over a regionfrom a flat surface portion of the alignment film 8 toward a portionabove the storage capacitive electrode 21. According to this embodiment,the angle of inclination of the inclined surface 8a, i.e., the angle ofinclination of the alignment film 8 with respect to the principal flatportion above the display electrode 4, is set to be not more than 10.5°,preferably not more than 7°. Thus, reverse orientation of liquidcrystals caused by the presence of the inclined surface 8a can beeffectively suppressed.

Another inclined surface 8b is formed on the alignment film 8, also inthe vicinity of the video line 1. This inclined surface 8b is set at anangle of inclination of not more than 10.5°, preferably not more than 7°similarly to the case of the aforementioned embodiment, therebyeffectively suppressing reverse orientation of the liquid crystalscaused by the presence of the inclined surface 8b, similarly to theembodiment shown in FIG. 1.

According to the present invention, as hereinabove described, the angleof inclination of the inclined surface formed on the alignment film dueto the presence of the electrode such as the storage capacitiveelectrode which is partially present under the display electrode or theelectrode such as the video line which is present on a side of thedisplay electrode is smoothed to be not more than 10.5°, preferably notmore than 7°, whereby formation of reverse regions can be effectivelysuppressed.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. An active matrix liquid crystal displaycomprising:a first substrate; a display electrode formed on said firstsubstrate; a video line electrode formed on a side of said displayelectrode on said first substrate; an insulating layer formed betweensaid display electrode and said video line, said insulating layer beinglarger than said display electrode and smaller than said video line inthickness; an alignment film formed to cover said display electrode; asecond substrate opposed to said first substrate; a counter alignmentfilm formed on a surface of said second substrate facing said firstsubstrate; and liquid crystals held between said alignment film and saidcounter alignment film, said alignment film having a surface inclinedfrom a flat surface portion above said display electrode toward aportion of said alignment film above said video line electrode, an angleof inclination of said inclined surface of said alignment film being setto be not more than 10.5 degrees with respect to said flat surfaceportion of said alignment film.
 2. An active matrix liquid crystaldisplay comprising:a first substrate; a display electrode formed on saidfirst substrate; a video line electrode formed on a side of said displayelectrode on said first substrate; an alignment film formed to coversaid display electrode; a BPSG layer and a SOG layer formed between saiddisplay electrode and said alignment film; a second substrate opposed tosaid first substrate; a counter alignment film formed on a surface ofsaid second substrate facing said first substrate; and liquid crystalsheld between said alignment film and said counter alignment film, saidalignment film having a surface inclined from a flat surface portionabove said display electrode toward a portion of said alignment filmabove said video line electrode, an angle of inclination of saidinclined surface of said alignment film set to be not more than 10.5degrees with respect to said flat surface portion of said alignmentfilm.
 3. An active matrix liquid crystal display comprising:a firstsubstrate; a display electrode formed on said first substrate; a storagecapacitive electrode consisting of a polycrystalline silicon layer,wherein said storage capacitive electrode is partially formed under saiddisplay electrode; an insulating layer comprising alternating BPSG andSOG layers, wherein said insulating layer is disposed between saidstorage capacitive electrode and said display electrode; an alignmentfilm formed to cover said display electrode; a second substrate opposedto said first substrate; a counter alignment film formed on a surface ofsaid second substrate facing said first substrate; and liquid crystalsheld between said alignment film and said counter alignment film, saidalignment film having a surface inclined from a flat surface portionabove said display electrode toward a portion of said alignment filmabove said storage capacitive electrode, an angle of inclination of saidinclined surface of said alignment film being set to be not more than10.5 degrees with respect to said flat surface portion of said alignmentfilm.
 4. The active matrix liquid crystal display in accordance withclaim 3, further comprising a substrate covering film disposed betweensaid polycrystalline layer and said first substrate.